Dosage forms, such as compressed tablets, chewable tablets, fast dissolving tablets, capsules, softgels, and gelcaps are known in the pharmaceutical arts. Production of these dosage forms is often carried out in steps. Some production steps are continuous, and others are carried out as “batch” processes. The distinction is that, in a continuous production step, the dosage forms can be fed to and withdrawn from a processing stage continuously, usually without any time limit, whereas in batch processing, a quantity of dosage forms is fed to a processing stage, and then processed and withdrawn.
In the manufacture of many of these dosage forms, it is common to coat pellets with films or with layers of films. In the case of pharmaceutical products, the coatings can have a number of purposes. The coatings can be cosmetic, pharmaceutically active, or otherwise functional. For example, a coating can be used to prevent a portion of a drug from being released in the form of dust. It can be used to mask an unpleasant odor or taste of the active drug, or of a filler or binder. It can be used to facilitate swallowing by providing the dosage form with a smoother and less absorbent outer layer. A coating resistant to gastric fluids can be used to prevent premature digestion of the contents of a dosage form. A coating can also control the rate of absorption of the drug by the small intestine. A coating can also be used to provide a dose of another drug in combination with the base dosage form. Finally, a coating can improve the appearance of the tablet, impart a distinctive color to the tablet for identification, and provide a printable surface.
Dosage forms are often coated using machines which spray a liquefied coating material onto the surfaces of the dosage forms while the dosage forms are in motion within a container. Examples of typical liquefied coating materials, include hydroxypropylmethylcellulose (HPMC) and starch-based materials. These coating materials may or may not include pigment,
Two common types of machines tumble tablets within a drum that rotates about a horizontal axis during the spraying process.
The coating step for pharmaceutical volume products is most often a batch process, and in the most commonly used batch process, a perforated pan coating machine is used. The perforated pan machine includes a rotating, perforated drum which rotates about a horizontal axis within a housing, and further includes a plurality of nozzles positioned within the drum. The nozzles create a spray of coating material within the drum so that dosage forms located within the drum will tumble about into and out of the spray pattern and, over a period of time, accumulate a coating on their surfaces.
Appropriate ducting is used to direct air through the housing of the perforated pan machine so that it passes through the perorated drum and reaches the dosage forms tumbling therein. The perforations of the drum expose the tumbling dosage forms to a current of air, resulting in more uniform drying. The drum further includes baffles, which enhance mixing of the dosage forms in order to improve the distribution of the material being sprayed onto the tablets.
Unfortunately, batch coating has drawbacks. For example, each of the various apparatuses employed in batch coating is housed in a separate clean room that must meet standards set by the Food and Drug Administration. This requires a relatively large amount of capital in terms of space and machinery.
Batch coating processes are also difficult to control because the control algorithms attempt to control the process toward a difficult-to-define endpoint, rather than control a continuous process where parameters can be controlled using feedback.
Heretofore, batch coating processes have inhibited manufacturers from interconnecting process stages, and from flexibly interconnecting continuous stages of various kinds and capabilities to meet manufacturing requirements. A process that would increase and streamline production rates by coupling continuous processing stages in line would provide many economic benefits, including a reduction in the size of facilities needed for mass production of pharmaceutical products. Generally, it would be desirable to create a continuous coating process for the formation of tablets and other dosage forms, so that linkages can be made with other similar or different operations such as tablet compression. By making such linkages, it will be possible to carry out dosage form production in an overall continuous process.
Continuous coating processes for dosage forms also exist. An example is the model CC-3015 continuous coater made by O'Hara Technologies of Richmond Hill, Ontario, Canada. These continuous coating processes utilize rotating cylinders, and are generally limited to relatively large throughput volumes. The reason is that there are practical limits on how close the spraying systems can be to the bed of pellets to be coated. The required spray-to-bed distance, and also the need to accommodate monitoring sensors in the vicinity of the product being coated, imposes a limit on how small the diameter of the cylinder can be, and therefore limits the ability of a manufacturer to scale down a continuous coating process to lower throughput volumes. Thus, while continuous coating is useful in the production of non-prescription products such as calcium supplements, antacids, and other products sold in high volumes, it is difficult to scale down a continuous coating machine to make it practical for use with lower throughput volumes such as in the case of most prescription drugs. Consequently, coating of many prescription drugs is still carried out in a batch mode.
Another problem common to the existing batch coating machines and continuous coating machines is that shear forces and stresses encountered by tablets in these machines can cause splitting or chipping of tablets, especially multi-layer tablets and tablets having less physically robust formulations.